Moshe Coll

Arthropod pest resurgence: an overview of potential mechanisms

Abstract The phenomenon of insecticide-induced resurgence of arthropod pests has long been known to occur in response to a reduction in natural enemy populations, releasing the pest population from regulation. However, studies of resurgent populations infrequently examine other mechanisms, although numerous alternative mechanisms such as physiological enhancement of pest fecundity, reduction in herbivore-herbivore competition, changes in pest behaviour, altered host-plant nutrition, or increased attractiveness may also cause, or enhance the probability of, resurgence. Additionally, many studies that have identified natural enemy mortality as the primary cause of resurgence do not document a priori regulation by natural enemies and, therefore, are correlative in nature. In this paper, a universal definition of resurgence is proposed and criteria for determining the occurrence of resurgence are listed. Both of these are essential to rigorous evaluation of this important phenomenon. Alternative mechanisms for resurgence and potential areas of future research are identified. It is argued that insecticide resistance is not a mechanism underlying resurgence; rather, it simply enhances the probability that resurgence may occur. The similarity of resurgence to some insect outbreaks is discussed. In some cases natural outbreaks differ only in the initiating factor. The importance of resurgence management to plant protection is that resurgence is totally contradictory to the intended outcome of insecticidal application. This conflict strengthens the need to identify specifically the causal factors for each case of resurgence in order to manage this detrimental phenomenon effectively.

Effect of Nitrogen Fertilization on Aphis gossypii (Homoptera: Aphididae): Variation in Size, Color, and Reproduction

Abstract The effect of nitrogen fertilization on Aphis gossypii Glover color and size, fertility, and intrinsic rate of increase (rm) was studied on cotton plants. Nitrogen fertilization treatments consisted of 0, 50, 100, and 150% of the agronomic recommended level. Adult and nymph densities, as well as rm, were positively correlated with nitrogen fertilization. Aphid body length, head width, and darkness of color were recorded in populations on cotton plants fertilized with 100% nitrogen or with no nitrogen fertilization. Aphids on nitrogen-fertilized plants were significantly bigger and darker. All body size and darkness of color measurements were positively correlated with aphid fecundity. It was also found that the nutritional quality of the host plant on which the parent generation feeds has a stronger effect on the aphids than that of the quality of their own food plants. This phenomenon may dampen the effect short-term fluctuations in host plant quality have on aphid performance. Results are discussed in the context of aphid population biology, aphid–plant interactions and aphid population management.

Feeding and ovipositing on plants by an omnivorous insect predator

Omnivory (i.e., feeding at more than one trophic level) is common in many ecological communities. To date, most studies of omnivory have focused on systems that include omnivores that feed on several prey items, primarily in aquatic systems. Yet, many terrestrial insect predators feed not only on prey but also on plants. The difference between systems with plant-feeding omnivores and those with exclusively prey-feeding omnivores calls for special attention. The first step towards understanding the interactions between plant-feeding omnivores and their prey is to determine how omnivores respond to variations in plant properties. In this study, I investigated two major aspects of the interactions between the plant-feeding predatory bug Orius insidiosus and four host plants of its prey; the behavioral aspect, in which plants are selected for oviposition and the physiological aspect, in which plants differ in their suitability for the insects growth, survival, and reproduction. No prey was offered to the omnivore during any of the experiments, but older nymphs and adults were fed prey eggs prior to their use in the experiments. Data show that O. insidiosus females almost completely rejected corn leaves for oviposition; nymph and adult survival was highest on bean; and female fecundity was higher on bean than tomato, pepper or corn foliage. the significance of the apparent ability of O. insidiosus to discriminate among plants and the observed correlation between oviposition preference and offspring performance in bean and in corn is discussed.

Putting plant resistance traits on the map: a test of the idea that plants are better defended at lower latitudes

• It has long been believed that plant species from the tropics have higher levels of traits associated with resistance to herbivores than do species from higher latitudes. A meta-analysis recently showed that the published literature does not support this theory. However, the idea has never been tested using data gathered with consistent methods from a wide range of latitudes. • We quantified the relationship between latitude and a broad range of chemical and physical traits across 301 species from 75 sites world-wide. • Six putative resistance traits, including tannins, the concentration of lipids (an indicator of oils, waxes and resins), and leaf toughness were greater in high-latitude species. Six traits, including cyanide production and the presence of spines, were unrelated to latitude. Only ash content (an indicator of inorganic substances such as calcium oxalates and phytoliths) and the properties of species with delayed greening were higher in the tropics. • Our results do not support the hypothesis that tropical plants have higher levels of resistance traits than do plants from higher latitudes. If anything, plants have higher resistance toward the poles. The greater resistance traits of high-latitude species might be explained by the greater cost of losing a given amount of leaf tissue in low-productivity environments.

Effects of Nonhost Plant on an Insect Herbivore in Diverse Habitats

Vegetation texture (i.e., plant density, species diversity, and structural com- plexity) may influence the abundance of a herbivore by affecting its movement, altering the suitability of host plants, and by changing the herbivores vulnerability to attack by natural enemies. We investigated these effects on the Mexican bean beetle (Epilachna varivestis) on snap bean (Phaseolus vulgaris) growing in high- and low-density monocultures and intercropped with short (0.5 m) or tall (1.2 m) corn plants (Zea mays). Beetle popu- lations consistently reached higher densities on beans in monocultures than on beans intercropped with tall corn. Neither bean plant density nor plant species diversity alone significantly affected beetle abundance. Instead, the presence of tall corn plants contributed most to lower bean beetle density in the tall corn-bean intercrop, primarily by reducing adult colonization. However, the tall corn also increased the suitability of intercropped bean plants to the beetles because adults preferred to feed on and larvae developed faster on beans in the tall corn-bean habitat. Host plant effects were independent of the influence of microclimate and risk of predation. Abundance of natural enemies of the bean beetle was low, and overall, predator density and bean beetle larval survival did not differ significantly among habitats. However, it is difficult to predict the effect of mortality factors, such as natural enemies, on bean beetle populations because larval mortality over time was affected by habitat type (i.e., there was a significant interaction between habitat type and time). Our results were partially consistent with the resource concentration hypothesis. Where- as Mexican bean beetles colonized bean monocultures more readily than they did tall corn- bean diculture, the presence of more suitable host plants in the diculture acted to increase, rather than decrease, bean beetle density in the tall corn-bean habitat. However, higher adult feeding preference and faster larval development on beans in the tall corn-bean habitat did not offset lower adult colonization in this habitat.

Population structure of the pestiferous moth Helicoverpa armigera in the Eastern Mediterranean using RAPD analysis

The genetic structure of the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), was studied in the eastern Mediterranean. Moths were sampled in six locations (five in Israel, and one in Turkey) and their genetic relationship was analysed using RAPD-PCR. Three 10-oligonucleotide primers revealed 84 presumptive polymorphic loci that were used to estimate population structure. Results reveal low level of genetic distances among Israeli and Turkish populations. The estimated values of FST and θ for the eastern Mediterranean populations were very low across all populations, indicating a high level of gene flow. Four distinct RAPD-product profile types were defined, and found in all Israeli and Turkish populations. Although no isolation by geographical distance was detected, topographical barriers may play a role in such isolation.

Effect of plants on the searching efficiency of a generalist predator: the importance of predator‐prey spatial association

In most studies of tritrophic interactions, the effect of plants on predators is confounded with changes in prey and predator behaviors after an encounter event. Here, we estimate how the effect of plants on prey distribution (in the absence of the predator) and on predator foraging behavior (in the absence of prey) may influence predation rate of Orius insidiosus (Say) (Heteroptera: Anthocoridae) in 11 plant by prey species combinations. The within‐leaf distributions of O. insidiosus and its prey overlapped most on bean plants. The predators foraging behavior (e.g., walking speed, turning rate) also differed among plant species. Simulations, using the prey distribution data and predators foraging patterns on leaf surfaces of each plant species, show that, overall, the searching efficiency of O. insidiosus was higher on leaves of bean and corn than of tomato. However, the predators searching efficiency was not consistent within plant species. Thus, the combined effect of plants directly on the predator and indirectly through the prey influenced the predators searching efficiency.

Movement of an insect parasitoid in simple and diverse plant assemblages

Abstract. 1. It has been proposed that herbivore populations are lower in diverse than in simple plant habitats because of greater abundance and/or higher efficiency of natural enemies in mixed plant stands. However, higher enemy colonization is expected in monorather than multispecific vegetation if the response of specialist natural enemies to habitat diversification is similar to that of monophagous herbivores.

Predator-prey association in mono- and dicultures: Effect of maize and bean vegetation

Abstract The effect of bean and maize vegetation on the abundance of prey, predators, and predation rate in larvae of the Mexican bean beetle ( Epilachna varivestis Mulsant (Coleoptera: Coccinellidae)) was investigated. Prey and predator densities were determined when bean and maize plants were grown alone (monocultures) and when bean plants were intercropped with tall or short maize plants (dicultures). On bean plants, overall densities of aphids, leafhoppers, and thrips and their predators did not differ between mono- and dicultures. Higher numbers of the predators Orius insidiosus (Say) (Heteroptera: Anthocoridae) and Coleomegilla maculata (De Geer) (Coleoptera: Coccinellidae) in maize than bean monocultures did not result in higher densities on bean plants in maize-bean dicultures. Only spiders and nabids (in some samples) were more abundant in dicultures. Data suggest that the predators do not aggregate in habitats with higher bean beetle densities. Nonetheless, the mortality of bean beetle larvae was density independent in bean monocultures and inversely density dependent in a maize-bean diculture. The results therefore suggest that predators have a greater effect on bean beetle populations in dicultures than in monocultures and they reinforce low bean beetle colonization in intercropped habitats.

Oviposition vs. offspring fitness in Aphidius colemani parasitizing different aphid species

We measured the acceptance and suitability of four aphid species [Aphis gossypii Glover, Myzus persicae (Sulzer), Rhopalosiphum padi (L.), and Schizaphis graminum (Rondani)] (Homoptera: Aphididae) for the parasitoid Aphidius colemani Viereck (Hymenoptera: Braconidae). Female parasitoids parasitized fewer R. padi than the other three aphid species, and fewer offspring successfully completed development in R. padi than in the other three host species. Sex ratios of emerging adults were more male‐biased from R. padi than from the other three aphid species, suggesting that R. padi is a poor quality host for this population of A. colemani. Ovipositing A. colemani encountered R. padi at a slower rate, spent more time handling R. padi, and parasitoid offspring died at a higher rate in R. padi compared to A. gossypii. Our results show that oviposition behavior and offspring performance are correlated. In each experiment, we tested the effect of the host species in which the parasitoids developed (parental host) on the number of hosts attacked, the proportion of each host species accepted for oviposition and the survival of progeny. Parental host affected maternal body size and, through its effect on body size, the rate of encounter with hosts. Other than this, parental host species did not affect parasitism.